Forage harvesters of the type to which the present invention pertains employ relatively heavy and large rotatable cutter heads having a plurality of knives thereon which are spaced even distances circumferentially. It is common practice to arrange said knives upon the periphery of the cutter heat at an angle to the axis thereof as well as at an angle to the shear bar, it being understood that the shear bar normally is mounted stationarily within the harvester in parallel relation to the periphery of the cutter head, whereby during the shearing operation, no sudden shock is imposed upon the knives of the cutter head or the shear bar as occurs when the rotatable knives and shear bar are mounted in parallel relationship with each other. It also is conventional at present to include a power-driven, rotatable grinding wheel as part of the standard equipment of a forage harvester. Guide means also are included adjacent the periphery of the cutter head in order that the grinding wheel may be moved in an axial direction across the cutting edge of each knife from one end to the other while the cutter head is being rotated by the prime mover of the harvester and the grinding wheel also is rotated by power derived from said prime mover.
It is appropriate to inspect the knives of the cutter head periodically to determine whether the same need sharpening and, in addition, after the same have been either partially or completely sharpened, inspection of the individual knives likewise is desirable. At present, such inspection is undertaken manually by an operator engaging each blade and pulling the cutter head stepwise in a suitable direction to permit adequate inspection of the cutting edges and bevelled surfaces immediately rearward of the cutting edges of the knives. Due to the fact that the cutter heads are large and heavy, considerable force is required to effect such rotation of the cutter head. In addition, there is a certain amount of possible danger that an operator's hand may be cut by the edges of the knives.
For an understanding of the details of the forage harvesters in which cutter heads of the type to which the present invention pertain, as well as the mechanism for operating the same, attention is directed to prior patents U.S. Pat. No. 3,751,859, in the name of P. K. Pedersen, dated Aug. 14, 1973, U.S. Pat. No. 3,793,792, in names of R. A. Wagstaff and R. W. Waldrop, dated Feb. 26, 1974; and U.S. Pat. No. 3,863,403, in name of P. F. Fleming, dated Feb. 4, 1975. In all of said previous patented structures, inspection of the cutter head is effected usually manually. In addition, said patents disclose cutter heads in which the knives are disposed at an angle to the axis of the cutter head, somewhat in a skewed manner, and guide means for the grinding wheels shown in said patents also is illustrated therein and it is to be noted that particularly in the first two patents auxilary means is required to effect desired biasing forces between the knives of the cutter head and the grinding wheel, said auxilary mechanism being somewhat awkward to manage as well as being provided solely for purposes of effecting such biasing action and not performing any other useful function incident to any other operational characteristics of the machine.